Answered: Combobox List - Virgin Line

Hello ,
Before starting I am sorry with my english.. I don't speak it well ..
So I have a problem with the Combobox in ExtJS4 .. I tried to add a virgin line in my combobox list but It's not ok .. Now i have the list with a virgin line but when I trie to select it I can't.. so if someone can help me or have an example pliz